1. Field of the Invention
Embodiments of the invention generally relate to a recovery method and system for delivering extracted benzene, toluene and xylene (BTX) from hydrocarbon gas streams. More particularly, embodiments of the invention relate to a recovery method and system for delivering an extracted BTX component from a BTX-rich hydrocarbon gas stream that includes contacting, for example, in an amine-free environment, a BTX-rich hydrocarbon gas feed stream with an aprotic solvent to produce a BTX-free gas and a BTX component.
2. Description of the Related Art
Gas streams in processing facilities, such as refineries, olefins plants, and other industrial settings sometimes contain aromatics, such as BTX. BTX is typically removed from the gas stream to avoid impacting the reliability of certain processing equipment in the path of the steam that may be sensitive to BTX. Moreover, when the gas stream is a sales gas used as fuel, such as by a utility or other energy generator, BTX components can negatively affect equipment handling the sales gas.
Fixed media adsorption is one technique used in conventional systems, as shown in FIGS. 1a and 1b, to remove BTX from a gas stream, where the media can be, for example, an activated carbon bed, as shown in FIG. 1a, a molecular sieve, as shown in FIG. 1b, or other adsorbent. Conventional adsorption methods using fixed media are typically expensive and require that the media be regenerated at some point to remove the adsorbed BTX. Regenerating adsorption media typically requires taking the media out of service for a period of time, or alternatively, a parallel circuit is required to continue operating, while the primary circuit is undergoing regeneration. Additionally, when regenerating the adsorption media, the removed BTX is contained in the regeneration fluid. Accordingly, a separate process is generally required to remove the BTX from the regeneration fluid. Regeneration fluids are often one of a regeneration gas or a regeneration steam. When regeneration steam is used, a separator is included that allows sour water to fall out of the flow, which can be sent to a treatment plant, while the removed BTX is part of a stream that is directed to a crude unit. In these conventional systems, while the BTX is removed from the gas stream, the extracted BTX component is consumed and therefore cannot be recovered for use as a petrochemical feedstock or for other commercial uses.
Extractive distillation is another technique used in conventional systems, as shown in FIGS. 1c and 1d, to remove BTX, but is limited to use for extracting BTX from a liquid stream, such as a refinery or petrochemical aromatic-containing liquid stream, for example, naphtha, which contains, non-aromatic hydrocarbons. In these conventional systems, as shown in FIGS. 1c and 1d, the BTX-rich liquid steam may be fed to a catalytic reformer to produce a reformate product containing C6 to C8 aromatics (BTX), paraffins, and heavier aromatics containing 9 to 12 carbon atoms. A solvent, for example, in aprotic (i.e., non-H+ donating ion) organosulfur compound, may be used to extract BTX from the BTX-rich liquid stream (e.g. platformate) using, for example, a contacting column, such as a liquid-liquid extraction unit, to generate a BTX-rich solvent from the bottom of the contacting column. The BTX-rich solvent is subsequently distilled using a distillation tower, where BTX is separated from the BTX-rich solvent.